FAILED: patch "[PATCH] net: usb: asix: hold PM usage ref to avoid PM/MDIO + RTNL" failed to apply to 5.15-stable tree

PATCH New [email protected] 2 participants 2 messages Oct 13, 2025 – Oct 14, 2025

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[email protected]

author maintainer

2025-10-13 11:48 UTC #0 lore raw

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 3d3c4cd5c62f24bb3cb4511b7a95df707635e00a
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2025101349-reptile-seldom-427d@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 3d3c4cd5c62f24bb3cb4511b7a95df707635e00a Mon Sep 17 00:00:00 2001
From: Oleksij Rempel <[email protected]>
Date: Sun, 5 Oct 2025 10:12:03 +0200
Subject: [PATCH] net: usb: asix: hold PM usage ref to avoid PM/MDIO + RTNL
deadlock
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Prevent USB runtime PM (autosuspend) for AX88772* in bind.

usbnet enables runtime PM (autosuspend) by default, so disabling it via the usb_driver flag is ineffective. On AX88772B, autosuspend shows no measurable power saving with current driver (no link partner, admin up/down). The ~0.453 W -> ~0.248 W drop on v6.1 comes from phylib powering the PHY off on admin-down, not from USB autosuspend.

The real hazard is that with runtime PM enabled, ndo_open() (under RTNL) may synchronously trigger autoresume (usb_autopm_get_interface()) into asix_resume() while the USB PM lock is held. Resume paths then invoke phylink/phylib and MDIO, which also expect RTNL, leading to possible deadlocks or PM lock vs MDIO wake issues.

To avoid this, keep the device runtime-PM active by taking a usage reference in ax88772_bind() and dropping it in unbind(). A non-zero PM usage count blocks runtime suspend regardless of userspace policy (.../power/control - pm_runtime_allow/forbid), making this approach robust against sysfs overrides.

Holding a runtime-PM usage ref does not affect system-wide suspend; system sleep/resume callbacks continue to run as before.

Fixes 4a2c7217cd5a ("net: usb: asix: ax88772: manage PHY PM from MAC")

Reported-by Hubert Wiśniewski <[email protected]>

Closes https://lore.kernel.org/all/[email protected] open here

Tested-by Hubert Wiśniewski <[email protected]>

Reported-by Marek Szyprowski <[email protected]>

Closes https://lore.kernel.org/all/[email protected] open here

Cc [email protected]

Signed-off-by Oleksij Rempel <[email protected]>

Link https://patch.msgid.link/[email protected] open here

Signed-off-by Paolo Abeni <[email protected]>

drivers/net/usb/asix_devices.c +29 -0

index 792ddda1ad49..85bd5d845409 100644
@@ -625,6 +625,21 @@ static void ax88772_suspend(struct usbnet *dev)
 		   asix_read_medium_status(dev, 1));
 }
 
+/* Notes on PM callbacks and locking context:
+ *
+ * - asix_suspend()/asix_resume() are invoked for both runtime PM and
+ *   system-wide suspend/resume. For struct usb_driver the ->resume()
+ *   callback does not receive pm_message_t, so the resume type cannot
+ *   be distinguished here.
+ *
+ * - The MAC driver must hold RTNL when calling phylink interfaces such as
+ *   phylink_suspend()/resume(). Those calls will also perform MDIO I/O.
+ *
+ * - Taking RTNL and doing MDIO from a runtime-PM resume callback (while
+ *   the USB PM lock is held) is fragile. Since autosuspend brings no
+ *   measurable power saving here, we block it by holding a PM usage
+ *   reference in ax88772_bind().
+ */
 static int asix_suspend(struct usb_interface *intf, pm_message_t message)
 {
 	struct usbnet *dev = usb_get_intfdata(intf);

@@ -919,6 +934,13 @@ static int ax88772_bind(struct usbnet *dev, struct usb_interface *intf)
 	if (ret)
 		goto initphy_err;
 
+	/* Keep this interface runtime-PM active by taking a usage ref.
+	 * Prevents runtime suspend while bound and avoids resume paths
+	 * that could deadlock (autoresume under RTNL while USB PM lock
+	 * is held, phylink/MDIO wants RTNL).
+	 */
+	pm_runtime_get_noresume(&intf->dev);
+
 	return 0;
 
 initphy_err:

@@ -948,6 +970,8 @@ static void ax88772_unbind(struct usbnet *dev, struct usb_interface *intf)
 	phylink_destroy(priv->phylink);
 	ax88772_mdio_unregister(priv);
 	asix_rx_fixup_common_free(dev->driver_priv);
+	/* Drop the PM usage ref taken in bind() */
+	pm_runtime_put(&intf->dev);
 }
 
 static void ax88178_unbind(struct usbnet *dev, struct usb_interface *intf)

@@ -1600,6 +1624,11 @@ static struct usb_driver asix_driver = {
 	.resume =	asix_resume,
 	.reset_resume =	asix_resume,
 	.disconnect =	usbnet_disconnect,
+	/* usbnet enables autosuspend by default (supports_autosuspend=1).
+	 * We keep runtime-PM active for AX88772* by taking a PM usage
+	 * reference in ax88772_bind() (pm_runtime_get_noresume()) and
+	 * dropping it in unbind(), which effectively blocks autosuspend.
+	 */
 	.supports_autosuspend = 1,
 	.disable_hub_initiated_lpm = 1,
 };

Sasha Levin

maintainer

2025-10-14 16:56 UTC #1 lore raw

PATCH 1/1 net: usb: asix: hold PM usage ref to avoid PM/MDIO + RTNL deadlock

From: Oleksij Rempel <[email protected]>

[ Upstream commit 3d3c4cd5c62f24bb3cb4511b7a95df707635e00a ]

Prevent USB runtime PM (autosuspend) for AX88772* in bind.

Holding a runtime-PM usage ref does not affect system-wide suspend; system sleep/resume callbacks continue to run as before.

Fixes 4a2c7217cd5a ("net: usb: asix: ax88772: manage PHY PM from MAC")

Reported-by Hubert Wiśniewski <[email protected]>

Closes https://lore.kernel.org/all/[email protected] open here

Tested-by Hubert Wiśniewski <[email protected]>

Reported-by Marek Szyprowski <[email protected]>

Closes https://lore.kernel.org/all/[email protected] open here

Cc [email protected]

Signed-off-by Oleksij Rempel <[email protected]>

Link https://patch.msgid.link/[email protected] open here

Signed-off-by Paolo Abeni <[email protected]>

[ adapted to phylib-only ]

Signed-off-by Sasha Levin <[email protected]>

---
 drivers/net/usb/asix_devices.c | 35 +++++++++++++++++++++++++++++++++-
 1 file changed, 34 insertions(+), 1 deletion(-)

drivers/net/usb/asix_devices.c +34 -1

index 97d2037e7fee7..2e22be26921b8 100644
@@ -608,6 +608,21 @@ static void ax88772_suspend(struct usbnet *dev)
 		   asix_read_medium_status(dev, 1));
 }
 
+/* Notes on PM callbacks and locking context:
+ *
+ * - asix_suspend()/asix_resume() are invoked for both runtime PM and
+ *   system-wide suspend/resume. For struct usb_driver the ->resume()
+ *   callback does not receive pm_message_t, so the resume type cannot
+ *   be distinguished here.
+ *
+ * - The MAC driver must hold RTNL when calling phylink interfaces such as
+ *   phylink_suspend()/resume(). Those calls will also perform MDIO I/O.
+ *
+ * - Taking RTNL and doing MDIO from a runtime-PM resume callback (while
+ *   the USB PM lock is held) is fragile. Since autosuspend brings no
+ *   measurable power saving here, we block it by holding a PM usage
+ *   reference in ax88772_bind().
+ */
 static int asix_suspend(struct usb_interface *intf, pm_message_t message)
 {
 	struct usbnet *dev = usb_get_intfdata(intf);

@@ -809,7 +824,18 @@ static int ax88772_bind(struct usbnet *dev, struct usb_interface *intf)
 	if (ret)
 		return ret;
 
-	return ax88772_init_phy(dev);
+	ret = ax88772_init_phy(dev);
+	if (ret)
+		return ret;
+
+	/* Keep this interface runtime-PM active by taking a usage ref.
+	 * Prevents runtime suspend while bound and avoids resume paths
+	 * that could deadlock (autoresume under RTNL while USB PM lock
+	 * is held, phylink/MDIO wants RTNL).
+	 */
+	pm_runtime_get_noresume(&intf->dev);
+
+	return 0;
 }
 
 static int ax88772_stop(struct usbnet *dev)

@@ -827,6 +853,8 @@ static void ax88772_unbind(struct usbnet *dev, struct usb_interface *intf)
 
 	phy_disconnect(priv->phydev);
 	asix_rx_fixup_common_free(dev->driver_priv);
+	/* Drop the PM usage ref taken in bind() */
+	pm_runtime_put(&intf->dev);
 }
 
 static void ax88178_unbind(struct usbnet *dev, struct usb_interface *intf)

@@ -1452,6 +1480,11 @@ static struct usb_driver asix_driver = {
 	.resume =	asix_resume,
 	.reset_resume =	asix_resume,
 	.disconnect =	usbnet_disconnect,
+	/* usbnet enables autosuspend by default (supports_autosuspend=1).
+	 * We keep runtime-PM active for AX88772* by taking a PM usage
+	 * reference in ax88772_bind() (pm_runtime_get_noresume()) and
+	 * dropping it in unbind(), which effectively blocks autosuspend.
+	 */
 	.supports_autosuspend = 1,
 	.disable_hub_initiated_lpm = 1,
 };

Signature · 1 line

2.51.0